I do different things depending on the file type:
1) Pictures - have their own hard drive which I keep in my fire proof box with important paper documents. I reupload my pictures once a month, as long as I've added to the files. (More often around Christmas, less often in the summer.) I don't put these on the cloud because there's so many. (At least 45gigs at this point.)
2) Writing - whatever I'm currently working on gets emailed to myself as it's one of the fastest ways to back up small files. It will also eventually go onto an external hard drive and on the cloud. I personally use Google Drive because I get free storage space and I'm familiar with it, though there are plenty of equally reasonable cloud options on the market. Often freshly editing pieces will get posted to my Crit Group on FB. It's a great way to share files while serving as an extra backup.
3) Games or software - I only back up my personal save files, not the base software. If I'm getting a new computer it's best to redownload those anyways. This also makes the backing up go a lot faster, though it does take some knowledge of which files do what.
What do you do to back up your files?